19 March 1999

Soil N sufficient for crops, trials reveal

APPLYING nitrogen as a starter fertiliser for maize may be a thing of the past for many growers.

New research suggests soil levels of available N – which rise significantly during the growing season – are sufficient to satisfy the crops requirement on many soils, says Ian Richards of Ipswich-based Levington Agriculture.

Its results from three years of MAFF-funded trials assessing optimum N levels for maize found most crops do not respond to applications ahead of drilling. This included nitrogen supplied in FYM and bagged fertiliser.

Researchers suggest crops did not respond to extra N because levels of available N in soils at sites countrywide increased by an average of 160kg/ha N (128 units/acre) in June with or without pre-drilled nitrogen. This is about the time maize growth accelerates and nitrogen is needed.

"We are not sure why or what is causing the sudden release of soil N," says Dr Richards, but it could reduce the need to apply N when drilling this season on many soils.

To determine whether maize needs extra N he suggests sampling soils for nutrients when maize is at the four leaf stage. "Where extra N is required, it can be applied at this growth stage without restricting crop development.

"As a guide, average dry matter yields of maize should be multiplied by 12 to give the amount of N required. For example a 12t/ha DM crop will remove 144kg/ha N. Where soil sampling suggests the amount amount of available N is less than this, extra fertiliser is needed," says Dr Richards. A typical dressing at this level might be 60kg N/ha (48 units/acre).

Where nutrient levels need replenishing ahead of drilling – usually following cereals – and FYM and/or slurry have been applied this season, ADASs soil scientist Brian Chambers advises considering checking soil N levels because of increased leaching risks after high winter rainfall.

"The fact there will have been losses is unquestionable. But its not just ploughed in muck; considerable ammonia losses may have occurred from muck and slurry on the soil surface," says Dr Chambers.

He recommends testing nutrient levels tested at a soil depth of 60cm (23in) on individual fields. Where extra N is needed, it should not exceed MAFFs recommendation of 60kg/ha (48 units/acre) for maize on nitrogen-hungry soils.

Where N indices of one or two exist, usually following grass, applications at drilling should be 40kg/ha (32 units/acre) and 30kg/ha (24 units/acre) respectively, says Dr Chambers.

"It is also important to ensure adequate supply of phosphorus near the roots to stimulate development. Fortunately losses of P and K will be minimal, despite poor conditions," he says. &#42

Get maize off to a good start with our maize establishment

special, which looks at agronomy issues including new

fertiliser recommendations, why compaction risks are

greater after last winter, changes to pest control and

disease risks attributed to K zeae. Edited by Simon Wragg

Beware post-drilling leatherjackets

PRODUCERS ploughing in grass leys ahead of maize should look for high numbers of leatherjackets which may re-emerge after drilling and affect vulnerable maize seedlings, says ADAS pest specialist Jon Oakley.

Mr Oakley says the mild, damp autumn and winters mean leatherjacket numbers are rising, especially in the north. "Watch out for the dark grey beetle-like pests," he advises.

While ploughing will bury leatherjackets with grass and trash, they will re-emerge once the vegetative material has rotted, he warns. "Before you know it they will pop out of the ground just when maize seedlings have emerged. Little can be done ahead of drilling.

"The first sign, which can appear quickly, is keeled-over seedlings." He advises producers who identify a leatherjacket risk ahead of ploughing to remain vigilant. Walking newly drilled crops regularly to identify seedling damage will pay, he says.

Where damage is identified, treat crops with an appropriate post-emergence pesticide. But choice of spray is limited with some gamma-HCH (gamma-col) products losing approval for post-emergence application; chlorpyrifos (Dursban) can still be used, he says.

"There should not be too many other pest problems as the UK is too far north for many of the maize bugs, such as the European corn borer. Frit fly is the main concern, but most imported seed will have been treated.

"Pre-emergence treatments for Frit fly are available, but these can be costly. Alternatively, consider applying chlorpyrifos at the two leaf stage." &#42

No benefit for IACS producers

PRODUCERS growing maize on IACS registered land are unlikely to benefit from Agenda 2000 reforms unless the government agrees to a combined base area for maize and cereals.

According to a MAFF spokeswoman, until that agreement is made maize growers in England will continue to receive payments of about £77/ha (£31/acre) instead of full arable aid payments of £235/ha (£95/acre), at last weeks k value.

The decision not to combine base areas will be reviewed by the government and industry consultation is likely, she adds.

The NFU is against a combined base area for England – although this already exists for Scottish and Welsh growers – as area aid payments to arable producers could fall by up to 2%.

Despite the NFUs resistance, Maize Growers Association former chairman Gordon Tweddle is to lobby government officials and MPs on behalf of growers to have a single base area introduced. "Maize growers should have a combined base area and the government is thinking about the options," he says.

But MAFF says if Agenda 2000 proposals are ratified and there is a cut in intervention prices for cereals, there will be a small rise in area aid payments for maize. MAFF forecasts suggest this could be up to £17/ha (£7/acre). &#42

Assess failure risk

FAVOURABLE conditions for drilling maize in marginal areas over the past few years has increased its popularity, but the risk of crop failure still needs to be assessed carefully.

According to SACs head of farming systems, Dave Roberts, while maize grown at Crichton Royal, Dumfries, last year achieved reasonable yields, poor weather prevented it from maturing. As a result, starch and energy levels were lower than expected.

"It was a straightforward problem of not having sufficient heat last season," he says. "There can be such a variation in local growing conditions, particularly in marginal areas, that our advice to growers is still to check carefully whether maize can be grown," advises Dr Roberts.

Dorset-based agronomist Ken Tuffin agrees. Over the past few warmer years, many producers have been able to grow maize successfully in marginal areas, but this wont be the case each season, he warns. &#42